dummy in MyKSPConverged

[Matthew Knepley]

On Mon, Sep 7, 2009 at 2:01 AM, Klaij, Christiaan <C.Klaij at marin.nl> wrote:

> Matt,
>
> Thanks for your answer!
>
> dummy is defined as a PETSc integer inside MyKSPConverged, so why can't I
> set it to 0? I know it's not useful because it's just a dummy and nothing
> happens with it, but setting it shouldn't crash the code, right? Also, if
> setting it changes the basic definition of PETSC_NULL_OBJECT shouldn't you
> get a SEGV as well, or at least some kind of trouble?
>

dummy is something *you passed in* earlier in the code, and you passed in
something that should not change. I
do not know why you are getting an SEGV (I do not get one), but I do know
you should not change this for the
code to function correctly.

  Matt


> Chris
>
>
>
> Message: 5
> Date: Fri, 4 Sep 2009 10:49:25 -0500
> From: Matthew Knepley <knepley at gmail.com>
> Subject: Re: dummy in MyKSPConverged
> To: PETSc users list <petsc-users at mcs.anl.gov>
> Message-ID:
>        <a9f269830909040849t7a8dd52dwc7fa33c6a0d313f7 at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> On Fri, Sep 4, 2009 at 10:35 AM, Klaij, Christiaan <C.Klaij at marin.nl>
> wrote:
>
> >   Hello,
> >
> > With the new version 3.0.0-p8, if I assign a value to the dummy in
> > MyKSPConverged at the end of src/ksp/ksp/examples/tutorials/ex2f.F, I get
> a
> > segmentation fault (this didn't happen with version 2.3.3-p13). Any idea
> > why?
> >
>
> 1) I do not get a SEGV
>
> 2) You should not be setting this at all. You pass in PETSC_NULL_OBJECT,
> which means you are changing the definition of that
>    basic thing in PETSc. This can produce undefined results.
>
>  Matt
>
>
> > $ tail ex2f.F
> >       else
> >         flag = 0
> >       endif
> >       ierr = 0
> >       dummy = 0
> >
> >       end
> > $ ./ex2f -my_ksp_convergence
> > [0]PETSC ERROR:
> > ------------------------------------------------------------------------
> > [0]PETSC ERROR: Caught signal number 11 SEGV: Segmentation Violation,
> > probably memory access out of range
> > [0]PETSC ERROR: Try option -start_in_debugger or
> -on_error_attach_debugger
> > [0]PETSC ERROR: or see
> >
> http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html#Signal[0]PETSC<http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html#Signal%5B0%5DPETSC>
> > ERROR: or try http://valgrind.org on linux or man libgmalloc on Apple to
> > find memory corruption errors
> > [0]PETSC ERROR: likely location of problem given in stack below
> > [0]PETSC ERROR: ---------------------  Stack Frames
> > ------------------------------------
> > [0]PETSC ERROR: Note: The EXACT line numbers in the stack are not
> > available,
> > [0]PETSC ERROR:       INSTEAD the line number of the start of the
> function
> > [0]PETSC ERROR:       is given.
> > [0]PETSC ERROR: [0] GMREScycle line 133 src/ksp/ksp/impls/gmres/gmres.c
> > [0]PETSC ERROR: [0] KSPSolve_GMRES line 228
> src/ksp/ksp/impls/gmres/gmres.c
> > [0]PETSC ERROR: [0] KSPSolve line 308 src/ksp/ksp/interface/itfunc.c
> > [0]PETSC ERROR: --------------------- Error Message
> > ------------------------------------
> > [0]PETSC ERROR: Signal received!
> > [0]PETSC ERROR:
> > ------------------------------------------------------------------------
> > [0]PETSC ERROR: Petsc Release Version 3.0.0, Patch 8, Fri Aug 21 14:02:12
> > CDT 2009
> > [0]PETSC ERROR: See docs/changes/index.html for recent updates.
> > [0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
> > [0]PETSC ERROR: See docs/index.html for manual pages.
> > [0]PETSC ERROR:
> > ------------------------------------------------------------------------
>
> dr. ir. Christiaan Klaij
> CFD Researcher
> Research & Development
> mailto:C.Klaij at marin.nl
> T +31 317 49 33 44
>
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-- 
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener
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